Tony Blair was "tearing his hair out" over his inability to influence the Pentagon over postwar planning in Iraq, Lady Morgan, his former political secretary, has said in an interview with the Guardian.

"We could talk to the US state department and to the president, but we had no leverage over the defence department, and he [Donald Rumsfeld, the former US defence secretary] had been given the power to make decisions," she said.

"It was up to Bush to do the right thing and be in charge, but he was not. Sometimes he [Blair] was tearing his hair out".

Lady Morgan said George Bush was "straight to deal with", and many of the best meetings with him were when he and Mr Blair were one to one."

She added: "That is why Tony went to Washington so much. The video conference was no substitute."

Leading Labour figures spoke openly yesterday for the first time about Iraq as Mr Blair set out his departure timetable.

Lady Morgan said Mr Blair thought hard about postwar planning and was not so distracted by the need for a parliamentary majority for the war that he did not consider what might happen in Iraq after the war. "Tony gripped himself about this. He had a feel for it," she said. "I think he thought that ... if he had been in charge, we would not have been in this mess. He could see what needed to be done but he did not have the levers."

Lady Morgan said Mr Blair thought about resigning because he could not see himself ever being freed from allegations that he had deliberately misled the public over the war.

Mr Blair's officials have previously been reticent about discussing disputes between him and Mr Bush over the war. The two men will meet in Washington next week to discuss the situation in Iraq.

In a separate interview for Radio 4's World at One, Lady Morgan said: "The actual operation of the war and the postwar planning was done by Donald Rumsfeld and I don't think George Bush was running Donald Rumsfeld ... The fundamental problem is that it [Iraq] has become a place where terrorists from every major group are now operating."

Alastair Campbell, Mr Blair's former director of communications, also conceded, for the first time, that postwar planning had gone wrong. "The military part was done well. Subsequent to that there have been enormous difficulties. I would put that down to Donald Rumsfeld," he said. But he added that the buck in any country stopped with the leader.

Geoff Hoon, the former defence secretary, has told the Guardian, in a separate interview, that postwar planning went wrong partly because they planned for the wrong crisis and had not anticipated the speed with which Saddam's regime collapsed. Lord Kinnock, the former Labour leader, said yesterday he could not understand "the nature of the association with George Bush, particularly when it was evident that the Americans had made no effective preparation for conditions after the war."